This sample chapter covers the following topics that you need to master for the CCNP BCMSN exam: Layer 2 Switch Operation, Multilayer Switch Operation, Tables Used in Switching, and Troubleshooting Switching Tables.

Tables Used in SwitchingThis section explains how tables of
information and computation are used to make switching decisions. Coverage
focuses on the Content Addressable Memory table, involved in Layer 2 forwarding,
and the Ternary Content Addressable Memory, used in Layers 2 through 4
packet-handling decisions.

Troubleshooting Switching TablesThis section reviews the
Catalyst commands that you can use to monitor the switching tables and memory.
These commands can be useful when troubleshooting or tracing the sources of data
or problems in a switched network.

To have a good understanding of the many features that you can configure on a
Catalyst switch, you should first understand the fundamentals of the switching
function itself.

This chapter serves as a primer, describing how an Ethernet switch works. It
presents Layer 2 forwarding, along with the hardware functions that make
forwarding possible. Multilayer switching is also explained. A considerable
portion of the chapter deals with the memory architecture that performs
switching at Layers 3 and 4 both flexibly and efficiently. This chapter also
provides a brief overview of useful switching table management commands.

"Do I Know This Already?" Quiz

The purpose of the "Do I Know This Already?" quiz is to help you
decide if you need to read the entire chapter. If you already intend to read the
entire chapter, you do not necessarily need to answer these questions now.

The 12-question quiz, derived from the major sections in the "Foundation
Topics" portion of the chapter, helps you determine how to spend your
limited study time.

Table 3-1 outlines the major topics discussed in this chapter and the "Do
I Know This Already?" quiz questions that correspond to those topics.

The goal of self-assessment is to gauge your mastery of the topics in this
chapter. If you do not know the answer to a question or are only partially sure
of the answer, you should mark this question wrong. Giving yourself credit for
an answer you correctly guess skews your self-assessment results and might
provide you with a false sense of security.

Which of these performs transparent bridging?

Ethernet hub

Layer 2 switch

Layer 3 switch

Router

When a PC is connected to a Layer 2 switch port, how far does the
collision domain spread?

No collision domain exists.

One switch port.

One VLAN.

All ports on the switch.

What information is used to forward frames in a Layer 2 switch?

Source MAC address

Destination MAC address

Source switch port

IP addresses

What does a switch do if a MAC address can't be found in the CAM
table?

The frame is forwarded to the default port.

The switch generates an ARP request for the address.

The switch floods the frame out all ports (except the receiving
port).

The switch drops the frame.

In the Catalyst 6500, frames can be filtered with access lists for
security and QoS purposes. This filtering occurs according to which of the
following?

Before a CAM table lookup

After a CAM table lookup

Simultaneously with a CAM table lookup

According to how the access lists are configured

Access list contents can be merged into which of the following?

A CAM table

A TCAM table

A FIB table

An ARP table

Multilayer switches using CEF are based on which of these
techniques?

Route caching

Netflow switching

Topology-based switching

Demand-based switching

Which answer describes multilayer switching with CEF?

The first packet is routed, and then the flow is cached.

The switch supervisor CPU forwards each packet.

The switching hardware learns station addresses and builds a routing
database.

A single database of routing information is built for the switching
hardware.

In a switch, frames are placed in which buffer after forwarding decisions
are made?

Ingress queues

Egress queues

CAM table

TCAM

What size are the mask and pattern fields in a TCAM entry?

64 bits

128 bits

134 bits

168 bits

Access list rules are compiled as TCAM entries. When a packet is matched
against an access list, in what order are the TCAM entries evaluated?

Sequentially in the order of the original access list.

Numerically by the access list number.

Alphabetically by the access list name.

All entries are evaluated in parallel.

Which Catalyst 3550 command can you use to display the addresses in the
CAM table?

show cam

show mac address-table

show mac

show cam address-table

You can find the answers to the quiz in Appendix A, "Answers to Chapter
'Do I Know This Already?' Quizzes and Q & A Sections." The
suggested choices for your next step are as follows:

7 or less overall scoreRead the entire chapter. This
includes the "Foundation Topics," "Foundation Summary," and
the "Q&A" section.

810 overall scoreBegin with the "Foundation
Summary" section and then follow up with the "Q&A" section at
the end of the chapter.

11 or more overall scoreIf you want more review on these
topics, skip to the "Foundation Summary" section and then go to the
"Q&A" section at the end of the chapter. Otherwise, move on to
Chapter 4, "Switch Configuration."